Video surveillance systems having multiple video cameras often comprise switching circuitry for selectively routing the video signals from the video cameras to a single viewing monitor. During this routing, if the selected video signals are not synchronized with respect to their vertical phase components (i.e., the components which initiate or start the video signals across the viewing monitor), significant distortion occurs. To avoid this, various procedures have been used to provide the needed vertical phase synchronization.
One form of vertical phase synchronization presently employed utilizes a dedicated reference signal to phase synchronize the vertical phase components of the various video signals. This reference signal is provided in common to the synchronization circuits which generate the synchronization signals for the video cameras developing the video signals. In this way, the vertical phase components of all the video signals are synchronized and little or no distortion occurs on the monitor when changing over from one video signal to another. However, this form of vertical phase synchronization is costly and labor intensive, since it requires the installation of a separate wire or a coaxial cable for carrying the dedicated reference signal to the synchronization circuits located at the video cameras.
A second form of vertical phase synchronization, known as linelock, utilizes the AC power line as a reference signal for the video camera synchronization circuits. Since the AC power line is usually already available for the purpose of general power distribution, no separate lines have to be installed and installation costs are thus reduced.
However, the AC power available at various points in a location is not necessarily at the same phase. For example, in a conventionally used three phase AC power distribution system, the phase of the AC power at any given location might be any one of the three different phases. Thus, in linelock systems, additional adjustments must still be made to compensate for the various phases of the AC power.
These adjustments are typically made at the video camera locations. Specifically, the synchronization circuits of the cameras must be manually adjusted to compensate for the phase differences of their respective AC power. This then causes the video signals of the cameras to become synchronized with respect to their vertical phase components.
As can be appreciated, having to adjust each synchronization circuit is labor intensive and costly. Accordingly, in many linelock systems, this adjustment is often neglected and the video signals are never vertically phase synchronized, resulting in distortion at the time of switching.
It is an object of the present invention to provide an improved synchronization method and apparatus for a video system.
It is also an object of the present invention to provide an improved video surveillance system wherein the vertical phase components of the video signals of the video cameras of the system can be remotely adjusted.
It is still a further object of the present invention to provide an improved video surveillance system which automatically synchronizes the vertical phase components of the video signals formed by the video cameras of the system.